1. Field of the Invention
The invention in general relates to the field of sonar and particularly to apparatus utilized for passive receiver beam formation.
2. Description of the Prior Art
Beamformer apparatus is utilized in conjunction with a transducer array to form one or more beams for detecting distant targets in the underwater environment.
In one type of system a circular or cylindrical array of transducer elements is utilized in the formation of a single beam which may be rotated around 360.degree.. A more common arrangement, particularly with digital beamformer apparatus, simultaneously generates a plurality of receiver beams which point in different azimuth directions around a full 360.degree., or lesser angle.
Use of a circular array of multiple transducer elements results in a large unacceptable backlobe which must be eliminated in order to achieve acceptable directivity.
One way of eliminating this large backlobe is by the incorporation of baffles for the individual elements or groups of elements which, when their individual responses are combined, produce patterns with the desired front to back ratio. The use of baffles, however, significantly increases the weight and size of the transducer array since a minimum separation between transducer elements of approximately .lambda./2 is required, where .lambda. is the wavelength of the center frequency of interest of acoustic energy being detected. At low frequencies the value of .lambda. can be quite large, making the array unmanageable for certain deployment vehicles. To this end the array may be made collapsable and then expanded to full size only after deployment from the carrier vehicle. In addition, the baffle arrangement presents transducer mounting problems as well as machining problems for the baffle itself.
The present invention presents an arrangement which eliminates the need for baffles and allows a smaller collapsed diameter transducer array to be utilized without sacrificing directivity or detection capabilities when expanded after deployment.